The use of holograms as a security device is well established in the field of security documents, such as banknotes, passports, cheques, share certificates and the like. Holograms are, potentially, less challenging to counterfeiters to replicate because they are, relatively, well known and, relatively, well understood.
In order to reduce the risk of counterfeiting, many advances have been made in the field of holograms. However, these technological advances are, generally, in the area relating to metallic and reflective holograms. To increase the level of security in holograms, that is, to make counterfeiting or replication difficult, the complexity of the hologram design can be increased or a covert feature, such as a polarization layer within a diffractive hologram, is added. Polarization features require a reflective backing, and are only suitable for reflective holograms.